A contemporary topic of interest is that of so-called “Unmanned Air Vehicles” (UAVs), or “drone aircraft”, especially the smaller “Micro Air Vehicle” variety with wingspans on the order of 10 cm to 100 cm. A significant challenge facing such UAVs is providing them with the ability to operate in near-Earth environments with various levels of autonomy. One method of providing such relative depth information is with the use of optical flow. Optical flow is the apparent visual motion seen from an imager or eye that results from relative motion between the imager and other objects or hazards in the environment. Refer to the book The Ecological Approach to Visual Perception by John Gibson for an introduction to optical flow. Consider a UAV flying forward above the ground. The optical flow in the downward direction is faster when the ground is closer, thus optical flow can provide information on the terrain shape below. Optical flow in the forward direction indicates the presence of obstacles from which the UAV must turn. Finally, the same optical flow sensing can provide information on rotation and translation, allowing it to detect and respond to turbulence.
Further examples on how optical flow can be used for obstacle avoidance are discussed in the paper “Biologically inspired visual sensing and flight control” by Barrows, Chahl, and Srinivasan and the Ph.D. dissertation “Mixed-Mode VLSI Optical Flow Sensors for Micro Air Vehicles” by Barrows. The application of optical flow to robotics and other fields is a mature art. Many other papers and book sections are available in the open literature on how to use optical flow for various applications.
As set forth in earlier U.S. patents and other publications, techniques exist to fabricate optical flow sensors that are small, compact, and sufficiently light to be used on UAVs. Particularly relevant U.S. patents include U.S. Pat. Nos. 6,020,953 and 6,384,905. Particularly relevant books include Vision Chips by Moini and Analog VLSI and Neural Systems by Mead. Particularly relevant other publications include “Mixed-mode VLSI optical flow sensors for in-flight control of a micro air vehicle” by Barrows and Neely and the above-referenced Ph.D. dissertation by Barrows. Other relevant prior art is listed in the references section below.
Note that although this document discusses optical flow and optical flow sensors primarily in the context of UAVs, the subject matter and teachings below are applicable to all types of vehicles, robotic systems, or other systems that contain optical flow sensors or use optical flow sensing.